This invention relates to an image display method and an image display apparatus for implementing the method. More particularly, the invention relates to an image display method that can display an increased number of gradations or allows for enhanced reproduction of monochromatic image being displayed with a color display device in which a unit pixel consists of R, G and B cells. The invention also relates to an image display device for implementing the method.
The diagnostic images taken with medical diagnostic apparatus such as X-ray diagnostic apparatus, MRI (magnetic resonance imaging) apparatus and various types of CT (computed tomographic) apparatus are usually recorded on light-transmitting image recording films such as X-ray films and light-sensitive materials in film form and thereafter reproduced as light-transmissive images. The films showing the reproduced diagnostic images are set on a viewing device such as a so-called “Shaukasten”, a light box and a transilluminator and illuminated with backlight so that the images are viewed for diagnosis.
Conventionally, apparatus for medical diagnosis and measurement have a CRT (cathode-ray tube) display or LCD (liquid-crystal display) connected as a monitor for viewing the images taken and measured with such apparatus. Diagnosis is performed on the basis of the image output to the monitor or the diagnostic images yet to be output on films are checked, adjusted or otherwise processed on the monitor.
The images taken with the medical diagnostic apparatus or those taken and measured with the apparatus for medical diagnosis and measurement are often reproduced on so-called “blue based” monochromatic films. The gradation resolution of the reproduced images is typically in 10 bits (providing 1024 gradations).
One problem is posed here. It is associated with the fact that CRTs usually display images at a gradation resolution of 8 bits and LCDs usually display images at a gradation resolution of 6 bits, sometimes in 8 bits if they are of the latest high-performance model. Thus, whichever of the monitors in current use display images with data having a lower gradation resolution than the image data that has been output after image taking and measurement with the above-described apparatus for medical diagnosis and measurement, that is to say, so-called “image data that cancellation of significant bits has occurred”. Therefore, this “cancellation of the significant bits of the image data” occasionally causes a kind of noise called “artefacts” in contour lines which are commonly called pseudo-contours. Such noise will reduce or spoil the reliability of diagnoses and must be eliminated from medical diagnostic images.
To deal with this problem, it has been proposed to use a display technique by time division (for example, frame rate control which is hereunder abbreviated as FRC). In this technique, 10-bit image data may be divided by four to give four frames of 8-bit image data which are displayed consecutively in increasing frequency to represent a 10-bit gradation in 8 bits. However, this approach suffers from the problem of flicker in the image for the very reason that FRC is performed.
In order to eliminate flicker, the frame frequency in FRC display has to be increased to permit high enough display switching. In practice, however, the driver IC for the monitor and the monitor itself are limited in response speed. This problem presents considerable difficulty in medical diagnostic applications where an increased number of pixels are used with a view to providing higher image quality by representation of a high-definition image such as QSXGA (2560×2048 pixels).